1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for an image pickup apparatus using a solid-state image pickup element, such as a video camera, an electronic still camera, a broadcasting camera, or a monitor camera, or an image pickup apparatus such as a silver-halide film camera.
2. Description of the Related Art
In recent years, an image pickup apparatus using a solid-state image pickup element, such as a video camera, a digital still camera, a broadcasting camera, or a monitor camera, as well as a silver-halide film camera has high performance, and the entire apparatus is downsized. Then, an image taking optical system used for the image pickup apparatus is required to be a high-resolution zoom lens having a short total lens length, a compact (small) size, and a high zoom ratio (high magnification ratio). As a zoom lens which meets the requirements, there is known a positive-lead type zoom lens having a lens unit having a positive refractive power disposed on an object side. As the positive-lead type zoom lens, there is known a zoom lens constituted of five lens units namely, first to fifth lens units having positive, negative, positive, negative, and positive refractive powers arranged in order from the object side to an image side.
In the zoom lens described in Japanese Patent Application Laid-Open Nos. 2000-180722 and 2000-231050, a second lens unit is moved to the image side during zooming from a wide angle end to a telephoto end, and a fourth lens unit is moved along a locus convex toward the image side.
Generally in a zoom lens, in order to realize a small size of the entire system and a high zoom ratio, a refractive power of a main magnification lens unit needs to be enhanced so that a movement amount of the main magnification lens unit in zooming is increased. However, when the refractive power of the main magnification lens unit is enhanced so as to increase the movement amount, a high zoom ratio can be realized easily, but aberration variation in zooming is increased so that it is difficult to obtain high optical performance over the entire zoom range.
In the five-unit zoom lens described above, in order to realize a high zoom ratio, for example, a zoom ratio of 50 or larger, a small size of the entire lens system, and good optical performance, it is important to set appropriately a refractive power of each lens unit, and a move condition or the like of each lens unit in zooming. In particular, it is important to set appropriately move conditions of the second and fourth lens units in zooming and a refractive power (inverse number of a focal length) of each of a first lens unit, the second lens unit, and a fifth lens unit. If these structures are not set appropriately, it is very difficult to realize a small front lens effective diameter, to secure a high zoom ratio, and to obtain high optical performance over the entire zoom range.